1. Field of the Invention
The present invention relates to a recording/reproducing apparatus and a tracking servo control method that carry out tracking to keep a magnetic head on a desired data recording track on a magnetic recording medium.
2. Description of the Related Art
As one example of this type of recording/reproducing apparatus, Japanese Laid-Open Patent Publication No. 2005-166115 discloses a hard disk drive apparatus (magnetic recording apparatus) constructed so as to be capable of carrying out a process that measures offsets to obtain offset information that is used for tracking servo control. This magnetic recording apparatus includes a discrete track-type hard disk (“magnetic recording medium”) where non-magnetic regions (“guard band parts”) are formed between tracks (“data recording tracks”) in discrete regions (“data track pattern regions”), a composite magnetic head including a reproducing head (“reproducing element”) and a recording head (“recording element”), a driving mechanism unit that moves the magnetic head over the magnetic recording medium between the inner periphery and the outer periphery, and a control unit that carries out overall control over the magnetic recording apparatus. The magnetic recording medium described above is provided with offset measuring regions that are disposed between the discrete regions and servo regions (servo pattern regions). The offset measuring regions are entirely constructed of a magnetic material without non-magnetic regions being formed therein.
When this magnetic recording apparatus is used, a measuring process that obtains the offset information is carried out first. More specifically, first the offset measuring regions on the magnetic recording medium are initialized and signals used to measure the offset (a measurement pattern: hereinafter referred to as “measurement signals”) are written into the offset measuring regions. When doing so, the measurement signals are written into the offset measuring regions using the recording head in a state where the reproducing head is being made on-track to the innermost data recording track, for example (i.e., a state where the reproducing head is positioned at positions with the same pattern radius (i.e., positions at the same distance from the pattern center) as the innermost data recording track). In this type of magnetic recording apparatus, when the magnetic head is moved to a data recording track in the inner periphery or the outer periphery of the magnetic recording medium, a center line of a data recording track will intersect a line that joins the center of the recording head in the recording width direction and the center of the reproducing head in the read width direction (as one example, a line that is parallel with the direction in which the arm extends), or in other words, a skew angle is produced for the magnetic head. Accordingly, when the reproducing head is being made on-track to a predetermined data recording track in the inner periphery or the outer periphery (that is, when the center of the reproducing head in the read width direction is aligned with the center of a data recording track in the track width direction (i.e., a track center)), the center of the recording head in the recording width direction will not be aligned with the track center of the data recording track, or in other words, the recording head will be off-track (a state where the recording head is “offset”). This means that the measurement signals are recorded at positions that are displaced from the track center by a distance in keeping with the amount by which the recording head is off-track (i.e., this amount being the “offset”).
Next, by reading the measurement signals from the offset measuring regions using the reproducing head, a position that is aligned with the center in the radial direction of a region where the measurement signals were written, that is, a position that is aligned with the center in the recording width direction of the recording head during the writes of the measurement signals is specified. More specifically, the measurement signals are read from the offset measuring regions while moving the reproducing head in steps by a predetermined distance in the radial direction of the magnetic recording medium. When doing so, if the reproducing head is located to the inside or outside of the region where the measurement signals were written, the output level (i.e., amplitude) of the reproducing signal for the read measurement signals will fall. On the other hand, if the center in the radial direction of the regions in which the measurement signals were written is aligned with the center in the read width direction (i.e., the radial direction) of the reproducing head, the output level of the reproducing signal for the read measurement signals will reach its maximum value. Accordingly, the control unit specifies the center position of the reproducing head at a point where the output level of the reproducing signal for the measurement signals reaches its maximum value as the center in the radial direction of the regions in which the measurement signals were written and obtains the distance between the specified center and the center of the reproducing head during the writes of the measurement signals (i.e., the track center of the data recording tracks) as the offset of the recording head with respect to the reproducing head.
This process for measuring the offset is carried out at intervals of several tracks, for example, from the inner periphery to the outer periphery of the magnetic recording medium. For data recording tracks where the process for measuring the offset is not carried out, the offset is obtained by an interpolation process using the offsets obtained for the data recording tracks located to the inside and the outside of such data recording tracks. By doing so, an offset (i.e., an optimal offset for each data recording track) is obtained corresponding to each data recording track from the inner periphery to the outer periphery of the magnetic recording medium and such offsets are stored in a storage unit of the magnetic recording apparatus as offset information to be used during tracking servo control.
When data is recorded on a magnetic recording medium in this type of magnetic recording apparatus, tracking servo control is carried out using the offset information stored in the storage unit. More specifically, in the magnetic recording apparatus described above, when data is recorded on a desired data recording track in the inner periphery of the magnetic recording medium for example, the control unit carries out a tracking servo control process that controls the driving mechanism unit to align the center of the recording head in the recording width direction with the track center of the desired data recording track in the discrete regions. When doing so, the control unit adjusts the head position of the magnetic head to the inside, for example, relative to a standard position (as one example, a track center of a data recording track set by a servo pattern) specified based on a servo signal read by the reproducing head when the magnetic head is passing above the servo region immediately before the discrete region where the recording head is to be made on-track. To adjust the head position, the control unit uses an adjustment, which has been calculated based on an offset stored in the storage unit (as one example, an adjustment that is equal to the offset) as offset information for the data recording track on which the recording head is to be made on-track, as a target value. By doing so, recording data is written as a magnetic signal with the recording head made on-track to the desired data recording track.